1. Field of the Invention
The present invention relates to a low boron containing E-glass composition. More specifically, the present invention relates to a glass composition which comprises a small amount of boron, and still maintains fiberization capability.
2. Description of the Related Art
For many years, the industry has prepared fiberglass and fiberglass products with a base glass composition of the “E-glass” type. “E” glass is generally described in U.S. Pat. No. 2,344,961, and the described glasses are typified by the composition listed below (with the constituents being in weight percent):
SiO252-56%Al2O312-16%CaO16-19%MgO 3-6%B2O3 9-11%
U.S. Pat. No. 2,571,074 describes a “modified E” glass, which is typically devoid of MgO, and with the CaO content much higher than a typical “E” glass. In general, the glasses have a composition as shown below (the percentages being weight percent):
SiO252-56%Al2O312-16%CaO19-25%B2O3 8-13%
U.S. Pat. No. 4,166,747 describes an E glass which attempts to lower the B2O3 content in the glass used to manufacture glass fibers in order to achieve reductions in batch costs. To compensate, the glass composition used has only a small quantity of MgO. In general, the glass has a composition as shown below (the percentages being in weight percent):
SiO2 54-55%, more preferably 54.2-55%Al2O3 13-14%CaO 22-24%, more preferably 22.1-23.2%MgO0.2-0.5%, more preferably 0.3-0.4%B2O35.5-6.8%, more preferably 6.5-6.8%
Thus, typical E-glass compositions used in the industry generally contained approximately 6% or more B2O3. As a result of this level of B2O3, abatement of E-glass furnaces is required to reduce particulate emissions into the environment. As a result of the challenging economics, and environmental issues, E-glass type fibers have been proposed that contain little or no B2O3, i.e., see, for example, WO 00/73231; WO 01/32576; U.S. Pat. Nos. 6,136,735 and 5,789,329. Benefits are claimed associated with lower abatement costs and lower batch costs due to boron-free base glass formulations.
The elimination of B2O3 in the base glass compositions, however, has resulted in increases in the high temperature viscosity (HTV) and liquidus temperature relative to standard E-glass containing 6% or more B2O3. HTV is the temperature at which the glass melt has a viscosity of 1000 poises. In the production of fiberglass, the glass melt in the bushing is typically maintained at 50-100° F. above the HTV for optimum fiberization efficiency. A glass composition with a higher HTV requires more energy to achieve this viscosity and therefore, incurs higher energy costs. The liquidus temperature is the highest temperature at which devitrification (crystallization) of the glass melt occurs. In fiberglass production, it is greatly preferred that the glass melt be maintained at a temperature at least 150° F. above the liquidus to avoid crystallization problems and consequently, lower fiberization efficiencies. It has been found that in the commercial production of E-glass fibers, fiberization efficiency is significantly reduced as the difference between HTV and liquidus (referred to as “delta”) falls below approximately 150° F.
Thus, it would be desirable to take advantage of the cost benefits associated with lower boron E-glass formulations, but avoid the disadvantages of crystallization and fiberization problems. The challenge in producing such a composition is developing the right combination of oxides that yields a glass with a suitable HTV and maintains a delta of at least 150° F., while utilizing a lower amount of boron. Providing such a glass composition would be of exceptional value to the industry.
Accordingly, it is an object of the present invention to provide such a glass composition which can be used to make useful continuous fiberglass strands, which process is more economic to make, yet avoids major manufacturing problems associated with crystallization of the glass.
This and other objects of the present invention will become apparent to the skilled artisan upon a review of the following description and the claims appended thereto.